Metallic gasket

ABSTRACT

A metallic gasket having a first seal line SL 1  arranged in a manner to encircle the peripheral edge of an exhaust gas hole  3 , a second seal line SL 2  arranged along the outer peripheral edge of a base plate  2 , and full beads  6, 7  formed each in a convex cross-section by bending the base plate  2  along both seal lines. Elastic sealing material  8  to  11 , the height of which is substantially equal to the height of a convex portion of the beads, are fixed to the convex portion and a flat surface continuous to the convex portion. The elastic sealing material on the flat surface is so arranged as to cover up to the opening mouth position of the exhaust gas hole  3  or a peripheral edge position of the base plate  2  and, furthermore, elastic material parts  12, 13  are filled in a concave portion of the bead on the reverse side of the convex portion. This structure of the gasket leads to cost reduction and enables the gasket to maintain a stable sealing performance for a long period of time.

TECHNICAL FIELD

The present invention relates to a metallic gasket sandwiched betweenopposing joint surfaces of a cylinder block and a cylinder head thatform an internal combustion engine for use in motorcycles, automobiles,industrial machines, and outboard engines to seal the above-mentionedjoint surfaces.

BACKGROUND ART

Among conventional metallic gaskets of this kind, there is one whichgasket described in Japanese Patent Laid-Open No. Hei 6-101761, forexample. As shown in FIG. 38, this metallic gasket comprises a baseplate made of a sheet of thin metal, and the base plate has a firstthickness-increased portion 52 formed by fitting a grommet, for example,on the peripheral portion of the base plate defining an opening, such asa combustion chamber opening, and a rubber bead 53 formed by baking arubber material so as to protrude from both surfaces of the base plate50 along a seal line extending in the vicinity of the outer periphery ofthe base plate 50. The metallic gasket also has a secondthickness-increased portion 54 formed by folding back part of theperipheral edge portion of the base plate 50, and a recoverable elasticbody 55 disposed between the grommet and both surfaces of the base plate50.

In other words, the outer peripheries of openings, such as an oil holeor a water hole, formed in the base plate 50 are sealed by surroundingthe openings with a rubber bead protruding from both surfaces of thebase plate 50, and the compression-deformed amount of the rubber bead 53is regulated by the thickness-increased portions 52, 53 to therebyprevent the rubber bead 53 from being broken. To prevent. breakdown ofthe rubber bead 53 under compression, the compression-deformed amount ofthe rubber bead 53 is normally set at a maximum of about 40% or less,for example.

As another conventional metallic gasket, there is one which is describedin Japanese Patent Laid-Open No. 2001-206687

As shown in FIG. 39, this metallic gasket has a firstthickness-increased portion 52 formed by folding back the peripheraledge portion on the combustion chamber opening 51 side of the baseplate, and inserting a shim plate 58 into the inside of the foldedportion, and a second thickness-increased portion 54 formed by foldingback part of the peripheral portion of an oil hole or the outerperipheral edge of the base plate, for example. In this metallic gasket,two lines of metal bead 60 in a convex-concave profile (a convex portionis formed similarly on both surfaces of the base plate 50) are formed bybending the base plate 50 in a manner to protrude on both surfaces ofthe base plate 50 between the first and second thickness-increasedportions 52, 54, and an elastic sealing material 61 is filled in theconcave portion on the reverse side of the metal bead 60. When it isdesired to provide a less expensive gasket, galvanized iron is used asthe material for the base plate 50.

In the former example of prior art, however, out of the thickness of therubber bead 53, only the amount of the thickness that extends beyond thethickness-increased portions 52 and 54 is compressed and deformed togenerate resilience to provide a seal. Since the rubber bead 53 needs tobe formed on a flat portion so as to protrude from both surfaces of thebase plate 50, the amount of rubber used to form the rubber bead 53 islimited, so that the compression-deformed amount has to be small.Consequently, the degree of demand for dimensional accuracy of therubber bead 53 is high, the amount of concurrent deformation is small,processing of the rubber bead 53 becomes difficult, and processingaccuracy becomes severe.

For example, if the thickness 0.7 t of the first thickness-increasedportion 52 is designated as TO and the thickness 0.4 t of the base plateis designated as T1, the height T2 protruding to one side from the baseplate is

T2 = (T0 T1) 2 + compression-deformed amount = 0.15 + 0.15 = 0.4 (whichmeans the compression-deformed amount of 40% max.) = 0.21

Therefore, the protruding amount of the rubber bead on one side of thebase plate is 0.21 mm. Although there is a large difference between thethickness 0.7 t of the first thickness-increased portion and thethickness 0.4 t of the base plate, the rubber bead 53 has a very smallamount of rubber and therefore its compression-deformed amount is small;therefore, the rubber bead 53 becomes hard to process, and theprocessing accuracy becomes stricter as mentioned above.

The rubber bead 53 and a recoverable elastic bodies 55 in the end faceof the first thickness-increased portion 52 and the firstthickness-increased portion, directly exposed to cooling water, areliable to rusting or water absorption, thus increasing chances ofdeterioration in performance and degeneration in quality.

As described above, when a rubber bead 53 is formed on a flat surface ofthe base plate 50, supposing that a metallic gasket is interposedbetween the joint surfaces of a cylinder head and a cylinder block, forexample, a difference in thermal expansion between the cylinder head andthe cylinder block gives rise to a dislocation, which causes a shearingforce to be applied along the surface of the base plate 50, increasing apossibility of the rubber bead 53 separating from the base plate 50.

Since there is a gap between the base plate and each of the jointsurfaces in the region from the water hole to the seal line, if coolingwater other than specified is used, the base plate from the water holeto the seal line is susceptible to corrosion by the cooling water otherthan specified.

Further, in the region between the outer peripheral edge and the sealline (the position where the rubber bead 53 is formed) of the base plateexclusive of the folded-back portion (the second thickness-increasedportion 54) of the peripheral portion of the base plate 50, becausethere is a gap between both side surfaces of the base plate and each ofthe joint surfaces of the base plate 50, assuming that the metallicgasket is used in a outboard engine, filthy water or briny waterexternally enters the above-mentioned gap, giving rise to corrosion ofthe joint surfaces of parts of cast iron or aluminum and the exposedportions of the gasket base plate 50.

Further, since cooling water directly contacts the firstthickness-increased portion 52 formed by the folded-back metal and thefolded-back grommet on the combustion chamber opening 51 side at hightemperature, boiled water generates air bubbles inhibit the coolingeffect, increasing chances of overheat. On the other hand, since coolingwater directly contacts the rubber seal line, alcohol content orethylene glycol in cooling water causes corrosion or swelling to thewhole of the rubber bead 53, thus reducing durability.

In the latter example of prior art, the metallic gasket comprises afirst thickness-increased portion 52 formed by folding back the wholeperipheral edge on the combustion chamber side of the phase plate toseal off a high-pressure gas, and a second thickness-increased portion54 to prevent the engine from deformation and also to protect the bead60 (including the elastic sealing material 61) from excessivecompression. Since the second thickness-increased portion 54 is formedby partly folding back the outer peripheral edge portion, in the regionfrom the seal line by the bead 60 disposed near the outer peripheraledge of the base plate 50 or on the inner side of the bolt to the outerperipheral edge of the engine, a gap occurs on both surfaces of the baseplate by an amount corresponding to the rubber thickness between theseal area joint surfaces) of the engine and the surfaces of the gasket.

Therefore, assuming that the gasket is used in an overboard motor or thelike, it occurs that filthy water or briny water splashes and enters theabove-mentioned gap, and because the engine radiates heat to the sealarea of the engine of cast iron or aluminum and the exposed portions ofthe gasket base plate 50, the adhesion of briny water or the like causescorrosion.

As the engines which use the above-mentioned metallic gasket are reducedin size and weight, the deck width for the seal area of the enginebecomes narrower, and it becomes difficult to secure a space for forminga wide metal bead 60 in a wide, undulated structure protruding on bothsurfaces of the base plate 50 in addition to the width of thefolded-back portion along the peripheral edge of the combustion chamberopening. This can be said of the region around the openings, such asbolt holes, water holes and oil holes. As the engines that uses metallicgaskets become smaller and lighter, a problem is that it becomesdifficult to adopt the metallic gasket structure of the prior art (thelatter example).

Since the elastic sealing material 61 is used only in the concaveportion in contrast to the present patent application, if the hardnessof the base plate is low, when the elastic sealing material 61 isdeformed in compression, the metal bead 60 is likely to deform in amanner to warp in the through-thickness direction, and when thisdeformation occurs, this leads to a decrease in sealing pressure by aamount corresponding to the deformation.

Further, another example of the conventional metallic gasket isdisclosed in Japanese Patent Laid-Open 2001-173791, for example.

As shown in FIG. 40, this metallic gasket comprises two base plates 50.

More specifically, out of the two base plates 50, a thickness-increasedportion 52 is formed at the edge portion on the combustion chamberopening 51 side of a thicker base plate (upper base plate). A base-platebead 53 of a convex structure is formed on each of the two base plates50 in a position on the outer side of the thickness-increased portion 52and at a height higher than the thickness-increased portion 52. Themetallic gasket is composed by stacking two base plates 50 in such a waythat the convex portion sides of the two base-plate beads 53 face eachother. Further, the concave portions facing outside are filled with anelastic sealing material 54.

When the metallic gasket is disposed between opposing joint surfaces ofa cylinder block and a cylinder head and fastened with clamping bolts,the base-plate beads 53 are compressed and deformed down to thethickness of the thickness-increased portion around the inner peripheraledge of the combustion chamber opening and simultaneously the elasticsealing material 54 filled in the concave portion is compressed anddeformed to seal a combustion gas, oil, and cooling water pressures by asealing pressure from a composite spring made up of the spring force ofthe base-plate bead 53 and the spring force of the elastic sealingmaterial 54. Needless to say, there are conventional metallic gasketswithout any elastic sealing material 53 filled in the concave portionand also there are conventional metallic beads made up of a single pieceof base plate.

In this conventional metallic gasket (Refer to FIG. 40), however, thebase-plate bead 53 and the elastic sealing material 54, when deformed byfastening, jointly generate a resilience to apply a required sealingpressure along the seal line.

However, when the base plate 50 is formed by metal plate of low hardnessto prevent fatigue failure and reduce cost of the base plate 53, in theabove metallic gasket, when bolts are fastened and the elastic sealingmaterial 54 of the concave portion of the bead is compressed anddeformed, an external force is applied such that the base plates 50 andthe base-plate beads 53 are compressed and deformed in a manner to warpin the through-thickness direction. Since the base plates 50 are formedof metal of low hardness as mentioned above, the beads have a lowshape-retaining force and accordingly the base plate 50 have aninsufficient deformation-preventive force and hence a low sealingproperty.

By repeated load by repetition of operation and stoppage of the engine,after a long period of use, problems arise, such as a decrease in axialtension of the clamping bolts, changes with time of the base-plate bead53 on the base plate 50, or deterioration in the elastic sealingmaterial 54 of the concave portion of the bead; therefore, the sealingsurface pressure is likely to drop. Such problems tend to occurparticularly at overhanging parts on the outer side of the clampingbolts.

When the elastic sealing material 54 is formed by baking in the concaveportions of the base plates, even if the elastic sealing material 54 athigh temperature is filled in the concave portions, it changes in volumeby an amount of thermal expansion during subsequent cooling and beingleft open, the center portion of the elastic sealing material 54 wherethe thickness is at its highest contracts by an amount of thermalshrinkage. This is disadvantageous when the surface pressure drops asdescribed above. Such a phenomenon as this seems to be likely to occurparticularly when the gasket is mounted in the engine which has beenassembled with a weak fastening axial tension.

SUMMARY OF THE INVENTION

The present invention has been made to solve the above problems, and hasas its task to provide a metallic gasket capable of reducing cost andsecuring a stable seal performance for a long period of time.

To achieve the above task, there is provided a metallic gasketcomprising a base plate made of a thin metal plate, said base platehaving formed therein one or not less than two openings and a metal beadof a convex cross-section formed along seal lines by bending said baseplate in a through-thickness direction thereof, said metal bead beingdeformed in the through-thickness direction to seal opposing jointsurfaces when said metallic gasket is sandwiched between said jointsurfaces, wherein an elastic sealing material deformable undercompression in cooperation with deformation of said metal bead is fixedat least to a convex portion of said metal bead and is filled in aconcave portion on the reverse side of said convex portion, and theheight of said elastic sealing material on a surface of said convexportion side is made equal to or substantially equal to the height ofsaid convex portion, and wherein said elastic sealing materialdeformable under compression in cooperation with the deformation of saidmetal bead is fixed also to portions of said surface of the base platefacing at least one of an outer peripheral edge of said joint surfaceand an inner peripheral portion of an opening of said joint surfacelocated opposite said surface of the base plate.

Preferably, the largest bead width of the elastic sealing material onthe convex portion side is limited within 1.5 times the width of themetal bead with the exception of the bolted portions which are subjectedto a large pressure. It is necessary to apply more load to the baseplate as the width of the rubber bead becomes larger. From a viewpointof inhibiting an increase in load, it is desirable to limit the width ofthe bead of the elastic sealing material within 1.5 times the width ofthe metal bead as mentioned above. This does not apply to where a largeload is to be applied locally.

The thickness (height) of the elastic sealing material may be set from astandpoint that the compression-deformed amount is not more than 40%when the gasket is disposed between the joint surfaces, for example, avalue which does not give rise to compression fracture.

According to the invention, as a result of the metal bead being formedso as to be convex only on one surface of the base plate, the amount ofelastic sealing material can be more than when the rubber bead portionsare formed on both surfaces of the base plate, and consequently thecompression-deformed amount of the elastic sealing material is largerand the processing accuracy can be made less severe.

Further, since the elastic sealing material is fixed to the convexportion, in other words, to the inclined surface of the metal bead,there are less chances of the elastic sealing material separating fromthe base plate. Moreover, since the elastic sealing material is fixed tothe convex portion, the bead width is prevented from becoming wider thannecessary. The elastic sealing material on the convex portion serves toinhibit such a deformation of the base plate from warping by the elasticsealing material on the concave portion.

Further, since a required sealing pressure is generated by synergy ofthe resilience of the metal bead and the elastic resilience of theelastic sealing material fixed to the position of the metal bead, thehardness of material for the base plate can be lowered.

Since it is possible to obtain a wider sealing area by the elasticsealing material without widening the bead width more than necessary,the flaws, casting-blowholes and surface roughness on the joint surfacescan be absorbed, and the joint surfaces can be sealed satisfactorilywith a low surface pressure.

On the surface on the convex portion side of the base plate where a gapappears between the joint surfaces and the base plate, the elasticsealing material is fixed to a position that faces the outer peripheraledge portion on the opposing joint surface, for example, and thisprevents infiltration of water into the gap from the outside.

For the ease of process or the like, it is desirable that the elasticsealing material fixed to the convex portion of the metal bead isintegral with and continuous to the elastic sealing material facing theouter peripheral edge portion, for example, on the opposing jointsurface, but it is all right even if they are not continuous andseparate.

The height of the elastic sealing material facing the outer peripheraledge portion on the joint surface need not necessarily be equal orsubstantially equal to the height of the convex portion, and it does notmatter whether the former height is higher or lower than the elasticsealing material formed on the convex portion.

The invention is characterized in that the above-mentioned metal bead isa full bead or a half bead in a stepped form.

The invention is also characterized in that by partly varying at leastone of the height of the protrusion and the width of the metal width inthe extending direction of the metal bead, the sealing surface pressureis equalized in the extending direction of the bead.

According to the present invention, in low-rigidity portions on thejoint surface, the height of the bead is made relatively higher or thewidth of the bead is made wider to thereby increase a spring force ofthe bead there, and thus the sealing surface pressure is equalized inthe extending direction of the bead, in other words, along the seallines, and consequently a fastening force of the bolts can be utilizedefficiently.

In other words, by varying the height and the width of the beadaccording to the rigidity of the surface to be sealed on the jointsurface, the spring stress is varied which is generated by the elasticsealing material filled in the concave portion or by the elastic sealingmaterial fixed on the convex portion side of the bead, making itpossible to apply a necessary sealing pressure to the sealing area thatis low in rigidity.

The invention is also characterized in that the above-mentioned metalbead is formed along at least one of the inner peripheral edge of theopening in the base plate and the outer peripheral edge of the baseplate.

The invention is also characterized in that at least a part of the outerperipheral edge of the base plate extends beyond the opposing jointsurface to the outside.

According to this invention, by making the outer peripheral contour ofthe base plate larger than the joint surfaces, the elastic sealingmaterial fixed to the outer peripheral edge may face the outerperipheral edge of the opposing joint surface with an increasedtolerance, making it possible to securely prevent entry of salt water orthe like, for example, from the outside.

The invention is also characterized in that to the whole peripheral edgeor a part thereof in at least one of the inner peripheral edge of thesealing surface pressure formed in the base plate and the outerperipheral edge of the base plate, a thickness-increased portion isformed, on the base plate, with a thickness higher than the remainingareas of the base plate and lower than the convex portion of the metalbead to regulate the deformed amount in the through-thickness directionof the elastic sealing material.

According to the present invention, as a result of thecompression-deformed amount of the elastic sealing material beingsecurely regulated by the thickness-increased portion, the elasticsealing material can maintain its elasticity for a long period of time.

The invention is also characterized in that a thin corrosion-resistantfilm thinner than the above-mentioned elastic sealing material is fixedto the areas not covered with the elastic sealing material at least onone surface of the base plate.

According to this invention, even if salt water or liquid filthpenetrates in a gap between the base plate and the joint surfaces, atleast the surface of the base plate can be protected from corrosion.

The invention is also characterized in that a metallic gasket comprisinga base plate made of thin metal plate having at least a combustionchamber opening and a liquid hole, a thickness-increased portion formedat an inner peripheral edge on the combustion chamber opening side ofthe base plate, and a bead formed along a seal line for sealing bydeforming in the through-thickness direction, wherein at least a part ofthe seal line is arranged in a manner to encircle one or not less thantwo liquid holes, wherein a bead formed along the seal line encirclingat least the liquid hole comprises a metal bead formed in a convex formwith a height higher than the thickness-increased portion by bending thebase plate in the through-thickness direction, and a rubber bead made ofan elastic sealing material fixed to the surface on the convex portionside of the metal bead of the base plate and filled in a concave portionon the reverse side of the convex portion, wherein the elastic sealingmaterial on the surface of the convex portion side is fixed at least tothe surface of the convex portion of the metal bead and is arranged tobe equal or substantially equal in height to the metal bead, and whereina corrosion-resistant film is formed on the surface of the base platesurrounded by the bead formed along the seal line encircling the liquidhole on the convex portion side of the metal bead and the film has aheight lower than the height of the rubber bead.

The above-mentioned liquid hole is preferably a water hole.

According to this invention, the bead surrounding the liquid hole, suchas a water hole, prevents a liquid from the liquid hole leaching outover the bead.

At this time, by forming the bead as a composite bead of a metal beadand a rubber bead as mentioned above. In other words, as a result of themetal bead being formed as a convex form only on the top surface side ofthe base plate, the amount of the elastic sealing material is largerthan when a convex rubber bead is formed on both surfaces of the baseplate. Therefore, the compression-deformed amount of the elastic sealingmaterial is larger and the processing accuracy becomes less severe.Since the elastic sealing material is fixed to the convex portion, orthe inclined surface, of the metal bead, it is less likely for theelastic sealing material to separate from the base plate.

Further, because a required sealing pressure is generated by synergy ofthe resilience of the metal bead and the elastic resilience of theelastic sealing material fixed to the metal bead position, the hardnessof the base plate material can be decreased. Since it is possible toobtain a wide sealing area by an elastic sealing material, in otherwords, since an area seal by an elastic sealing material can be applied,the flaws on the joint surface, casting-blowholes, and processingsurface roughness can be absorbed, so that a satisfactory sealing can beobtained with a low surface pressure.

In the region from the liquid hole to the bead position, a gap occursbetween the surface of the base plate on the convex portion side of themetal bead and the joint surface, but since the corrosion-resistant filmis formed on the surface of the base plate, even if the liquid passingthrough the liquid hole is corrosive, the base-plate surface can beprevented from being corroded.

The invention is also characterized in that a thin, corrosion-resistantfilm is formed on the surface surrounded by the bead formed along theseal line on the concave portion side of the metal bead, and the film iscontinuous to the elastic sealing material filled in the concaveportion.

The metallic bead according to this invention is so structured as toprotrude only on one surface, but also on the surface of the base plateon the concave side of the metal bead and on the liquid hole side ratherthan on the bead side, there is a risk that the liquid flowing throughthe liquid hole will contact the surface of the base plate on theconcave side of the metal bead through the flaws on the opposing jointsurface or by vibration. In this invention, in the presence of thecorrosion-resistant film on the surface of the base plate on the concaveside, even if the liquid is corrosive, the surface of the base plate canbe prevented from being corroded.

The invention is also characterized in that a plurality of through-holesare formed at positions of the base plate surrounded by the bead formedalong the seal line encircling the liquid hole, and the films formed onboth surfaces of the base plate are connected through the plurality ofthrough-holes.

According to this invention, since the films on both surfaces of thebase plate are interconnected through the through-holes, the films areless liable to separate from the base plate. Note that the film on theconvex portion side of the metal bead is not in contact with the jointsurface, but the film on the concave side of the metal bead is incontact with the joint surface.

The invention is based on the structure set forth supra, and ischaracterized in that the film is also applied to the inside peripheralsurface of the liquid hole.

According to this invention, the inside peripheral surface of the hole,which would otherwise contact the liquid, is protected by the film. Atthis time, when the film is formed on both the front and reversesurfaces of the base plate, the all of those surfaces and end faces ofthe base plate on the liquid hole side rather than on the bead side areprotected by the film.

The invention is based on the structure set forth supra, and ischaracterized in that at least a part of the bead formed along the sealline encircling the liquid hole is arranged along the whole peripheraledge of the liquid hole, the elastic sealing material on the convexportion side is arranged up to the film continuous to the elasticsealing material on the convex portion side is applied to the insideperipheral surface of the liquid hole, and that the size of the liquidhole including an amount corresponding to the thickness of the film issubstantially equal to the size of the liquid hole open to the jointsurfaces to be sealed by the gasket sandwiched therebetween.

According to this invention, by forming the rubber bead close to theliquid hole, since the surface of the base plate on the convex portionside of the metal bead is protected by the rubber bead, the film is notrequired for the surface of the convex portion side.

The invention is also based on the structure set forth supra and ischaracterized in that the second thickness-increased portion is formedat a part of the outer peripheral edge of the base plate, and the sealline extending along the outer peripheral edge is arranged at the outerperipheral edge of the base plate or in the vicinity of the outerperipheral edge, excluding the second thickness-increased portion,wherein the bead formed along the seal line comprises a metal beadformed in a convex form higher than the thickness-increased portion bybending the base plate in the through-thickness direction, and a rubberbead made of an elastic sealing material fixed to the surface of theconvex portion side of the metal bead of the base plate and filled inthe concave portion and compressed and deformed in the through-thicknessdirection in cooperation with the deformation of the metal bead. theelastic sealing material on the surface of the convex portion side isfixed at least to the surface of the convex portion of the metal bead,and the height of the elastic sealing material is arranged to be equalor substantially equal to the height of the metal bead.

Since the bead structured as described is formed along the outerperipheral edge of the base plate, if there is a possibility that acorrosive liquid, such as salt water, enters from the outside, therubber bead formed along the outer peripheral edge prevents its entryfrom the outside. Above all, by forming the bead composed as described,even if there are flaws on the joint surfaces or vibration, because theelastic sealing material is in tight contact with the joint surface, asatisfactory sealing can be applied securely.

Therefore, the above-mentioned film need not be formed on the surface ofthe base plate between the bead encircling the liquid hole and the beadalong the outer peripheral edge of the base plate, because the surfacedoes not contact any corrosive liquid. It follows therefore that thejoint surface that faces the surface area of the base plate is alsoprotected from a corrosive liquid.

The invention is also based on the structure supra, and is characterizedin that the above-mentioned second thickness-increased portion isomitted, and to substitute for the second thickness-increased portion, awide-width portion is provided in part along the rubber bead in theextending direction of the rubber bead.

According to this invention, the second thickness-increased portion canbe omitted. Therefore, the gasket is so structured to be able tosubstitute for the second thickness-increased portion even when thesecond thickness-increased portion of metal cannot be formed for reasonsof space.

The invention is also based on the structure set forth supra, wherein acorrosion-resistant film is formed on the whole surface of the baseplate on the outer side of the seal line along the outer peripheral edgeof the base plate.

According to this invention, in an overboard motor or the like, if thereis a possibility that the outer peripheral edge of the base platecontacts a corrosive liquid, such as salt water, it is protected by theabove-mentioned film.

The invention is also based on the structure set forth supra, and ischaracterized in that one or not less than two lines of protrusions areformed along the seal line on at least one of the elastic sealingmaterial fixed to the surface of the above-mentioned convex portion sideand the surface of the elastic sealing material filled in theabove-mentioned concave portion.

The invention is also based on the structure described supra, and ischaracterized in that one or not less than two lines of protrusions areformed in the areas where the sealing surface pressure is relatively lowat least on one of the surface of the elastic sealing material fixed tothe surface of the convex portion side and the surface of the elasticsealing material filled in the concave portion.

The invention is also based on the structure set forth supra, wherein atleast one of the height and the width of each line of the protrusionsalong its extending direction is varied according to the sealing surfacepressure at the formed position of said protrusion, and as the sealingsurface pressure becomes small, a larger value is set for at least oneof the height and the width of the protrusions.

The invention is also based on the structure set forth supra, wherein aplurality of lines of protrusions are formed on at least one of thesurface of the elastic sealing material fixed to the convex portion sideand on the surface of the elastic sealing material filled in the concaveportion, and wherein in the plurality of lines of the protrusions, atleast one of a height of the protrusion and an area per unit length ofthe protrusion is varied according to the sealing surface pressure atthe formed position of the protrusion.

The invention is also based on the structure set forth supra, wherein aplurality of base plates are stacked in a multilayered structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view for explaining a metallic gasket according to afirst embodiment of the present invention;

FIG. 2 is a sectional view taken along the line A—A in Fig. 1;

FIG. 3 is a sectional view taken along the line B—B in FIG. 1;

FIG. 4 is a sectional view taken along the line B—B for explaining abead in a raised shape formed using half beads;

FIG. 5 is a plan view for explaining a metallic gasket according to asecond embodiment of the present invention;

FIG. 6 is a sectional view taken along the line A—A in FIG. 5;

FIG. 7 is a sectional view taken along the line B—B in FIG. 5;

FIG. 8 is a sectional view showing an engine in which a metallic gasketaccording to a second embodiment of the present invention is mounted;

FIG. 9 is another sectional view showing an engine in which a metallicgasket according to a second embodiment of the present invention ismounted;

FIG. 10 is a plan view for explaining a second thickness-increasedportion formed in one of bolt holes;

FIG. 11 is a sectional view taken along the line C—C in FIG. 10;

FIG. 12 shows a case where the second thickness-increased portion formedin a bolt hole is done away with;

FIG. 13 is a plan view for explaining a metallic gasket according to athird embodiment of the present invention;

FIG. 14 is a sectional view taken along the line A—A in FIG. 13;

FIG. 15 is a sectional view taken along the line B—B in FIG. 13;

FIG. 16 is a sectional view taken along the line C—C in FIG. 13;

FIG. 17 is a sectional view taken along the line D—D in FIG. 13;

FIG. 18 is a sectional view taken along the line E—E in FIG. 13;

FIG. 19 is a sectional view showing a case where the secondthickness-increased portion is replaced by a rubber bead;

FIG. 20 shows a case where the edge portion along the outer periphery ofthe base plate is also covered;

FIG. 21 shows a case where the edge portion along the outer periphery ofthe base plate is also covered;

FIG. 22 shows a case where the metal bead is formed as a half bead in araised shape;

FIG. 23 shows a case where the second thickness-increased portion isformed by metal;

FIG. 24 shows a case where the second thickness-increased portion isformed by metal;

FIG. 25 is a sectional view showing a bead according to a fourthembodiment of the present invention;

FIG. 26 is a sectional view showing a bead according to the fourthembodiment of the present invention;

FIG. 27 is a sectional view showing a bead according to the fourthembodiment of the present invention;

FIG. 28 shows another example of protrusion;

FIG. 29 shows yet another example of protrusion;

FIG. 30 shows a further example of protrusion;

FIG. 31 shows a still furthers example of protrusion;

FIG. 32 shows a still other example of protrusion;

FIG. 33 shows a yet further example of protrusion;

FIG. 34 shows an additional example of protrusion;

FIG. 35 shows an example of a half bead as the base plate;

FIG. 36 shows an example of a half bead as the base plate;

FIG. 37 shows a modification of the second elastic sealing material;

FIG. 38 is a diagram for explaining a conventional metallic gasket;

FIG. 39 is a diagram for explaining another conventional metallicgasket; and

FIG. 40 is a diagram for explaining a conventional metal bead.

BEST MODE FOR CARRYING OUT THE INVENTION

A first embodiment of the present invention will be described withreference to the accompanying drawings.

FIG. 1 is a plan view for explaining a metallic gasket according to thisembodiment. FIG. 2 is a sectional view taken along the line A—A in Fig.FIG. 3 is a sectional view taken along the line B—B in FIG. 1.

Description will start with the structure of the metallic gasketaccording to the first embodiment.

A metallic gasket 1 according to this embodiment is an example that boltholes are located along the outer periphery of the base plate, but thisis not intended to show a limitation. The base plate 2 of the metallicgasket 1 comprises metal plate, such as stainless steel plate, softsteel plate or aluminum plate.

In the middle of the base plate 2, as shown in FIG. 1, there is formed alarge exhaust gas hole 3 for an exhaust gas at high temperature to passthrough, and a first seal line SL1 is provided in a manner to endlesslyencircle the exhaust gas hole 3. On the outer side of the first sealline SL1, cooling water holes 4 for passing cooling water to cool theexhaust gas are formed at four positions in a manner to encircle theexhaust gas hole. Further, a second seal line SL2 is provided in anendless circle extending along the edge portion of the outer peripheryof the base plate 2. Bolt holes 5 for clamping bolts are formed at fourpositions on the outer side of the second seal line SL2.

As shown in FIGS. 2 and 3, full beads 6, 7 in a raised shape are formedby bending the base plate 2 along the first and second seal lines SL1,SL2.

Elastic sealing material 8 to 11 consisting of a rubber material, suchas fluororubber, NBR or silicon rubber or a resin material are fixed tothe surface of the base plate on the convex portion side of the fullbeads 6, 7, and a similar elastic sealing material 12, 13 are filled inthe concave portions on the reverse side of the convex portions of thefull beads 6, 7.

The elastic sealing material 8 to 11 fixed to the convex portion side ofthe full beads 6, 7 cover both sides across the width of the full beads6, 7, and are fixed to the flat surface of the base plate 2 continuousto the surface of the convex portion from both sides 8 a, 9 a, 10 a and11 a of the convex portion up to the nearby exhaust gas hole 3, coolingwater hole 4, or edge portion 2 a of the outer periphery of the baseplate 2. Reference numerals 8 b, 9 b, 10 b and 11 b denote the elasticsealing material parts fixed to the flat surface. Out of the two jointsurfaces between which the metallic gasket is disposed, the jointsurface SA1 faces the convex portion-side surface of the gasket and hasarranged thereon the opening end of the exhaust gas hole 3, the openingend of the cooling water holes 4, and all circumference of the outerperiphery of the joint surface SA1 . Elastic sealing material 8 b, 9 b,10 b and 11 b have been arranged on the surface of the base plate 2which faces the joint surface SA1 including the above-mentioned openingend of exhaust gas hole 3, opening end of the cooling water holes 4, andall circumference of the outer periphery of the joint surface SAI withwhich the elastic sealing material parts come into contact.

The height of the elastic sealing material 8 to 11 fixed to the convexportion side of the full beads 6, 7 is substantially equal to the heightof the convex portions of the full beads 6, 7, and the upper surface ofthe elastic sealing material parts is substantially parallel to the flatsurface of the base plate 2.

On the other hand, the amounts of the elastic sealing material 12, 13filled in the concave portions of the full beads 6, 7 are substantiallyequal to the capacities of the concave portions, and the upper surfacesof the elastic sealing material parts are substantially flush with theflat surface of the base plate 2.

In this embodiment, the molding of elastic sealing material 8 to 13 maybe performed to fix them to the surface of the convex portions and fillthem in the concave portions of the base plate 2. For this purpose,passages (not shown) for a molding material may be formed in the fullbeads 6 and 7 to enable simultaneous molding of the convex portion sideand the concave portion side of the beads.

As shown in FIG. 3, an elastic sealing material film 14 superior indurability and thinner than the above-mentioned elastic sealing materialis fixed to the flat surface on the convex portion side in the areabetween the cooling water holes 4. On the other hand, a thin elasticsealing material film 15 is fixed to the whole area of the flat surfaceon the concave portion side. A through-hole may be formed in the baseplate 2 to permit communication between the upper and lower elasticsealing material films 14, 15. When communication is provided betweenthe upper and lower sealing material films, those films 14, 15 are madeless susceptible to separation.

In the example of the metallic gasket 1, since the exhaust gas pressureto be sealed is lower than the pressure in the combustion chamber, athickness-increased portion is not formed to regulate the compressedamount of the elastic sealing material 8 to 13.

When a metallic gasket 1 structured as described is sandwiched betweenthe joint surfaces of the cylinder block and the cylinder head andfastened together, the elastic sealing material 8 to 11 fixed to theconvex portion side of the full beads 6, 7 and the elastic sealingmaterial 12, 13 filled in the concave portions are compressed anddeformed in the through-thickness direction in cooperation with the fullbeads 6, 7. Therefore, a dual seal is applied by an elastic resilienceof the full beads 6, 7 (including the elastic sealing material 8 to 13 )formed along the first seal line SLI and the second seal line SL2.

In the metallic gasket 1 structured as described, since the elasticsealing material 8 to 11 are fixed to the convex portions of the fullbeads 6, 7 and also the like sealing material parts 12, 13 are filled inthe concave portions in the full beads 6, 7, the elastic sealingmaterial protruding from the base plate 2 in the through-thicknessdirection is the sealing material only on the convex portion side of thefull beads 6, 7, in other words, only on one side of the base plate 2.

Therefore, if the height of the beads which are deformed after bolts arefastened is designated as t0, the height of the elastic sealing material8 to 11 fixed to the convex portions of the full beads 6, 7, forexample, is t0+the compression-deformed amount (t0

0.4 (40% max.)). If t0 is 0.5 mm, the height of the elastic sealingmaterial 8 to 11 is 0.7 mm from the above equation. Therefore, theelastic sealing material 8 to 11 on the convex portions of the fullbeads 6, 7 becomes large in quantity, which results in an increase inthe compression-deformed amount, making it easy to form the elasticsealing material 8 to 11 and making it possible to increase thethickness of the elastic sealing material parts, so that the amount ofconcurrent deformation becomes large and a large processing tolerancecan be set, making it possible to decrease production cost.

The elastic sealing material 8 to 11 fixed to both sides across thewidth of the convex portions of the full beads 6, 7 are exposed tocooling water at the areas thereof facing the water hole 4 side, and onthe other hand the elastic sealing material 12, 13 filled in the concaveportions of the full beads 6, 7 are covered with the full beads 6, 7 andtherefore are not exposed to cooling water, for which reason, theelastic sealing material parts are protected from deterioration and canmaintain a stable seal performance for a long period of time.

Further, a required sealing pressure is obtained by synergy of theresilience of the full beads 6, 7 and the elastic resilience of theelastic sealing material 8 to 11 fixed to the convex portion side andfilled in the concave portion side of the full beads 6, 7, a fact whichmakes it possible to decrease the hardness of the base plate 2,eliminate worries about fatigue failure of the beads 6, 7 of the baseplate 2, further absorb the engine vibration amplitude and the seal arearoughness, and thereby seal off cooling water pressure as well as oilpressure with less surface pressure.

Further, since a wide sealing area can be secured for the elasticsealing material 8 to 11 on the convex portion side of the beads 6, 7and for the elastic sealing material 12, 13 on the concave portion sideof the full beads 6, 7, the flaws on the joint surfaces and theblowholes that occur in casting and the working surface roughness can besealed satisfactorily with a low surface pressure. Furthermore, sincethe elastic sealing material 8 to 13 consist of an elastic substance(rubber-based material, above all else), the gasket factor is low, andtherefore a limited axial load can be utilized effectively in the areasunder adverse condition, so that total load can be decreased.Incidentally, since the elastic sealing material parts, which form therubber beads, are disposed chiefly on the convex portions of the metalbeads, the bead width need not be made wide unnecessarily.

At the full bead 7 formed along the second seal line SL2 on the outerperiphery side, since the surface pressure is at its highest where boltsare fastened and in their vicinity, it is possible to decrease thesurface pressure in the vicinity of where bolts are fastened by reducingthe width of the beads compared with other regions or by lowering theheight of the beads near the bolt holes to thereby equalize the sealarea pressure by the full bead 7 (including the elastic sealing material10, 11 ) along the second seal line SL2. By this equalization, the axialforce of the clamping bolts can be reduced.

In the above-mentioned metallic gasket 1, because the beads 6, 7protrude only on one surface of the base plate and also because theelastic sealing material 12, 13 are filled in the concave portions ofthe beads 6, 7, the whole surface of the base plate 2 on the concaveportion side of the beads 6, 7 are in contact with the correspondingjoint surface. For this reason, there is no place where a gap can occurbetween the above-mentioned surface of the base plate 2 and the jointsurface.

On the other hand, on the surface on the convex portion side of the bead6 formed along the first seal line, because there is provided theelastic sealing material 8 b equal in height to the bead 6 in the regionof the base plate which faces the inner peripheral end portionencircling the exhaust gas bore 3 on the opposing joint surface, whenthe bolts are fastened, the elastic sealing material 8 b is compressedand deformed to thereby seal the whole inner peripheral edge of theexhaust gas bore 3 by the elastic sealing material 8 b.

The elastic sealing material 11 b is provided on the outer peripheryside of the base plate 2 on the surface of the convex portion side ofthe bead 7 and at a position facing the outer periphery end portion onthe opposing joint surface. Therefore, as the elastic sealing material11 b is compressed and deformed when bolts are fastened, the wholeperipheral edge portion on the opposing joint surface is sealed by theelastic sealing material 11 b. Thus, water or the like is prevented fromexternally entering between the surface of the base plate 2 and thejoint surface SA1.

Further, since the elastic sealing material 9 b, 10 b are provided onthe inner peripheral region encircling each cooling water hole 4 on thesurface of the convex portion side of the beads 6, 7, the elasticsealing material 9 b, 10 b are in contact with the inner peripheralregion of each cooling water hole on the opposing joint surface, therebysealing the joint. Though there is not an elastic sealing material equalin height to the beads between the cooling water holes 4, the surface ofthe base plate 2 has the elastic sealing film fixed thereto and isthereby protected from cooling water. An elastic sealing material equalin height to the beads may be fixed to encircle the inner peripheraledge of each cooling water hole 4.

It is obvious from the foregoing, assuming that the metallic gasket 1 isused in an internal combustion engine of an overboard motor, forexample, salt water is often used as cooling water in an outboardengine, when stainless steel is used for the gasket, it is susceptibleto potential difference corrosion by cooling water, and when soft steelis used, it is liable to salt-water corrosion. However, when a metallicgasket 1 according to this embodiment is used and the bead structure andthe elastic sealing material layout described above are adopted, even ifless-expensive soft steel is used for cost reduction, salt water issealed off, thus preventing salt-water corrosion and improvingrust-preventive effects, and making it possible to prevent flangevibration amplitude, concurrent deformation by heat, and a decrease infastening axial tension. Further, when aluminum is used for the baseplate 2, there is no need to worry about salt-water corrosion, theelasticity can be obtained by the elastic sealing material 12, 13 filledin the concave portion of the convex full beads 6, 7 and by the elasticsealing material parts formed in the convex portion, and the sealingproperty can be secured by the elastic sealing material 8 a, 9 a, 10 a,and 11 a formed in the range in which the beads are covered.

Though the full beads 6, 7 as the convex type bead are illustrated inthe above embodiment, it is possible to adopt stepped half beads 6, 7 asshown in FIG. 4 where the seal area is narrow. In FIG. 4, the uppersurface of the inclined portion serves as the convex side surface of thebead, and the lower surface of the inclined portion serves as theconcave side surface, the height of the upper side elastic sealingmaterial 8, 11 is equal to the height of the bead, and the lower sideelastic sealing material 12, 13 are filled in up to the bottom surface.The operation and the effects are the same as described above.

A second embodiment of the present invention will be described withreference to drawings. Those parts of the second embodiment which areidentical with those of the first embodiment are designated by the samereference numerals.

FIG. 5 is a plan view for explaining a metallic gasket 1 according tothe second embodiment. FIG. 6 is a sectional view taken along the lineA—A in FIG. 5.

FIG. 7 is a sectional view taken along the line B—B in FIG. 5. FIGS. 8and 9 show two cases where a metallic gasket according to the secondembodiment is mounted in the engine.

The metallic gasket according to the second embodiment is a gasket whichis interposed between a cylinder block and a cylinder head.

Description will start with its structure.

As the base plate 2 of the metallic gasket 1 according to the secondembodiment, it is possible to show cases that the metal plate isstainless steel or soft steel. Here, suppose that soft steel is usedwith a view to providing a less expensive gasket.

The base plate 2 has a combustion chamber opening 20 provided and afirst thickness-increased portion 21 with the greatest thickest formedby upwardly folding back the inner peripheral edge portion of thecombustion chamber opening 20, thereby providing a difference inthickness from the remaining portions of the base plate. A secondthickness-increased portion 22 is formed by upwardly folding back a partof the outer peripheral edge of the base plate 2. The secondthickness-increased portion 22 is made thinner than the firstthickness-increased portion 21 by forging, for example. The foldedportion of the first thickness-increased portion 21 of the base plate 2is varied (inflected) in thickness along the peripheral portion of thecombustion chamber opening 20 in such a way that the folded portion inthe neighborhood of a bolt hole 5, which will be described later, ismade a thin portion and the folded portion in the region between thebolts 5 is made a thick portion. The total thickness of the thin portionof the first thickness-increased portion 21 is thicker than the totalthickness of the second thickness-increased portion 22.

A first seal line SL1 is provided in a manner to endlessly encircle thefirst thickness-increased portion 21 of the base plate 2. Holes, such aswater holes 23, an oil hole 24 and a chain chamber hole 25, are formedon the outer side of the first seal line SL1. A second seal line SL2 isprovided to extend along the outer peripheral edge of the base plate 2and also to surround the holes, such as the chain chamber hole 25.Reference numeral 26 denotes a bolt hole on the outer side of the secondseal line SL2.

As shown in FIGS. 6 and 7, convex cross-section full beads 6, 7 areformed by bending the base plate in a manner to extend along the firstand second seal lines SL1 and SL2.

Elastic sealing material 8 to 11, made of a rubber material, such asfluororubber, NBR and silicon rubber, a resin material, or the like, arefixed to the surface of the base plate 2 on the convex side of the fullbeads 6, 7, and like elastic sealing material 12, 13 are filled in theconcave portions located on the reverse side of the convex portions ofthe full beads 6, 7.

The elastic sealing material 8 to 11 fixed to the convex side of thefull beads 6, 7 are fixed to the surface of the base plate 2 at least tocover both sides across the width of the full beads 6, 7. Note that outof the elastic sealing material 8 to 11 provided on the convex side ofthe beads 6, 7, the sealing material 11 on the outer peripheral portionof the full bead 7 formed along the outer edge 2 a of the base plate 2is fixed up to the outer edge 2 a of the base plate 2, and also fixed tothe surface of the flat portion of the base plate 2 continuous to thesurface of the convex portion, while the elastic sealing material 11 bfixed to the surface of the flat portion can face the outer peripheraledge portion of the opposing joint surface.

In this embodiment, the outer edge 2 a of the base plate 2 is made toextend beyond the outer peripheral edge of the above-mentioned jointsurface to thereby absorb the forming error of the elastic sealingmaterial 11 that occurs during molding, with the result that the elasticsealing material 11 b can be securely positioned in a face-to-facerelation with the outer edge of the corresponding joint surface.

Out of the elastic sealing material parts provided on the convex portionsides of the beads 6, 7, in the region where the seal line SL2 a isformed surrounding the peripheral edge portion of the hole, such as thechain chamber hole 25, the elastic sealing material for the innerperipheral edge side of the full bead 7 is fixed to the flat surface ofthe base plate 2 continuous to the surface of the convex portion, thatis, up to the inner peripheral edge of the chain chamber hole 25 so thatthe elastic sealing material fixed to the above-mentioned flat surfacecan face the inner peripheral edge portion of the corresponding hole onthe opposing joint surface.

The height of the elastic sealing material 8 to 11 fixed to the convexportion side of the full beads 6, 7 is made equal to or substantiallyequal to the height of the convex portions of the full beads 6, 7, andthe upper surface of the elastic sealing material parts is madesubstantially parallel with the flat surface of the base plate 2.

On the other hand, the filled amounts of the elastic sealing material12, 13 filled in the concave portions of the full beads 6, 7 are madesubstantially equal to the capacities of the concave portions, and theirsurfaces are made substantially flush with the flat surface of the baseplate 2.

When a metallic gasket 1 structured as described is disposed between theopposing joint surfaces of a cylinder block 30 and a cylinder head 31and fastened with clamping bolts, the elastic sealing material 8 to 11fixed to the convex portions of the full beads 6, 7 and the elasticsealing material 12, 13 filled in the concave portions are compressedand deformed in the through-thickness direction in cooperation with thefull beads 6, 7, and at the end of fastening, the greatest surfacepressure concentrates on and the largest load acts on the firstthickness-increased portion 21 due to a difference in thickness betweenthe first thickness-increased portion 21 with the greatest thickness ofthe base plate 2 and the remaining portions.

Therefore, a threefold seal is applied, which comprises the largestsurface pressure at the first thickness-increased portion 21 and theelastic resiliences of the two lines of full beads 6, 7 (including theelastic sealing material parts on the convex and concave portions), andsimultaneously the stopper effect of the first thickness-increasedportion 21 prevents total collapse of the elastic sealing material 8, 9and 12 fixed to the convex side and filled in the concave side of thefull bead 6, and on the other hand, the stopper effect of the secondthickness-increased portion 22 prevents total collapse of the elasticsealing material 10, 11 and 13 fixed to the convex side and filled inthe concave side of the full bead 7.

Also in the metallic gasket 1 structured as described, since the elasticsealing material 8 to 11 are fixed to the convex portions and filled inthe concave portions of the full beads 6, 7, the elastic sealingmaterial that protrudes from the base plate 2 in the through-thicknessdirection is the elastic sealing material only on the convex side of thefull beads 6, 7, in other words, only on one side of the base plate 2.

Therefore, the height of the elastic sealing material 8 to 11 fixed tothe convex portions of the full beads 6, 7, for example, is t0+thecompression-deformed amount (t0

0.4 (40% max.), if the thickness of the folded-back portion of the baseplate 2 at the first thickness-increased portion 21 is designated as t0,and assuming that t0 is 0.5 mm, the height of the rubber bead is 0.7 mmfrom the above equation, which is twice as high as in prior art shown inFIG. 13

Therefore, the elastic sealing material 8 to 11 on the convex side ofthe full beads 6, 7 become large in quantity, which results in anincrease in the compression-deformed amount, making it easy to perform aforming process of the elastic sealing material parts, and making itpossible to increase the thickness of the elastic sealing materialparts, so that it becomes possible to set a large forming processtolerance and reduce manufacturing cost.

Further, the elastic sealing material 8 to 11 fixed to both sides acrossthe width the convex portions of the full beads 6, 7 are exposed tocooling water only at the areas facing the water hole 23 side. On theother hand, the elastic sealing material parts filled in the concaveportions of the full beads 6, 7 are covered with the full beads 6, 7 andare not exposed to cooling water, for which reason the elastic sealingmaterial parts are protected from deterioration and therefore canmaintain a stable seal performance for an extended period of time.

Further, a required sealing pressure is obtained by synergy of theresilience of the full beads 6, 7 and the elastic resilience of theelastic sealing material 8 to 13 fixed to the convex portion side andfilled in the concave portion side of the full beads 6, 7, a fact whichmakes it possible to decrease the hardness of the base plate 2,eliminate worries about fatigue failure of the beads 6, 7 of the baseplate 2, absorb the engine vibration amplitude and the seal arearoughness as well, and thereby seal off cooling water pressure and oilpressure with less surface pressure.

Further, since a wide sealing area can be secured for the elasticsealing material 8 to 11 on the convex portion side of the full beads 6,7 and also for the elastic sealing material 12, 13 on the concaveportion side of the full beads 6, 7, the flaws on the joint surfaces andthe blowholes that occur during casting and the working surfaceroughness can be sealed satisfactorily with a low pressure. Furthermore,since the elastic sealing material 8 to 13 consist of an elasticsubstance (rubber-based material, above all), the gasket factor is low,and therefore a limited axial load can be utilized effectively in theareas under adverse condition, s that total load can be decreased.

Further, the first thickness-increased portion 21 of the base plate 2 ismade a thin web area in the vicinity of the bolt holes 5, but it is madea thick web area between the bolt holes 5 such that the resilience ofthe first thickness-increased portion 21 during fastening the bolts isweak in the vicinity of clamping bolts whose fastening force is large,but the resilience is stronger in the region between the clamping boltswhose fastening force is relatively small. Consequently, the surfacepressure applied to the first thickness-increased portion 21 can beequalized in the circumferential direction of the combustion chamberopening 20 and the axial tension of the clamping bolts can be decreased,thus making it possible to effectively prevent deformation of theengine, especially, engines of low rigidity.

In recent engines, improvements have been made in downsizing, weightsaving and performance, and as lean fuel is burned for energyconservation, combustion chamber temperature has risen. To seal off highpressure gas, a high surface pressure is generated by providing thefirst thickness-increased portion 21 formed by folding back the innerperipheral edge on the combustion chamber opening 20 side of the baseplate as mentioned above. In this embodiment, by varying the thicknessin the circumferential direction of the first thickness-increasedportion 21, the fastening surface pressure along the peripheral portionof the hole for the combustion chamber opening is equalized, therebyimproving the efficiency of sealing a combustion gas.

In this embodiment, convex cross-section beads 6, 7 are provided ifnecessary in a manner to surround the first thickness-increased portion21 in the peripheral portion of the combustion chamber opening 20 andalso surrounding the oil hole 24, water holes 23, bolt holes 5 and achain chamber hole 25. With the convex cross-section beads 6, 7, thebead height or the bead width may be varied according to the rigidity ofthe joint surfaces at positions of contact to equalize the sealingpressure along the seal lines to thereby improve the seal efficiency.The sealing pressure can be equalized more easily by raising the beadheight or widening the bead width at positions where the rigidity isinsufficient and the surface pressure is weak.

As shown in the sectional view of FIG. 8 showing the gasket which ismounted, by fixing an elastic sealing material 11 b to the surface ofthe base plate 2 on the convex side, excluding the folded-back portion(the second thickness-increased portion 22 ) at the outer peripheraledge, the elastic sealing material 11 b, when compressed, is made tocontact the outer peripheral edge of the opposing joint surface 30 a toprevent filthy water or salt water or the like from entering from theouter peripheral end portion. More specifically, the base plate 2 ismade to extend beyond the joint surface 30 a of the cylinder head 30and, further, the elastic sealing material provided on the outer side ofthe convex portion of the bead, at which a gap occurs, is also made toprotrude from the seal area to thereby prevent infiltration of filthywater, salt water or the like. FIG. 9 shows a case where the beads 6, 7are provided with their convex side facing downward.

As shown in FIGS. 8 and 9, out of the opposing joint surfaces, the jointsurface on the smaller external profile side and the surface of the baseplate 2 on the convex side of the bead should preferably be designedsuch that they face each other.

FIG. 10 shows a case where the second thickness-increased portion 22 toregulate the compression-deformed amount of the elastic sealing materialis formed by folding back a part of the inner peripheral portion of theopening, such as a bolt hole 5 or an oil hole 6, instead of outerperipheral portion of the base plate 2. In this case, as shown in thesectional view taken along the line C—C in FIG. 11, it is possible toprevent corrosion of the base plate 2 by forming thin elastic sealingfilms 14, 15 in the regions, excluding the elastic sealing materialparts and the folded-back portions of the first thickness-increasedportion 21 and the second thickness-increased portion 22. Further, asshown in FIG. 12, it is possible to fix an elastic sealing material forthe convex side of the bead to the flat surface of the base plate 2 onthe bead 7 side along the second seal line SL2 to increase the area ofthe elastic sealing material, thereby getting rid of the secondthickness-increased portion 22, formed by folding back, which isprovided at a bolt hole 5, oil hole 6, or the like.

The structure of the metallic gasket 1 according to the presentinvention is not limited to the above-mentioned embodiment, but may bechanged with proper discretion without departing from the scope and thespirit of the invention.

For example, in the embodiment mentioned above, the secondthickness-increased portion 22 is made thinner by forging after foldingback the edge portion of the on the outer peripheral side of the baseplate 2. As an alternative for this, for example, the secondthickness-increased portion 22 may be formed by attaching, by weldingfor example, a shim plate thinner than the base plate 2 to the outerperipheral region of the base plate 2 to thereby omit theabove-mentioned forging of the second thickness-increased portion 22.Further, a shim plate may be included in the folded portion of the firstthickness-increased portion 21 to thereby omit the forming of the secondthickness-increased portion 22.

Further, in the embodiment mentioned above, the firstthickness-increased portion 21 is formed by folding back the innerperipheral end portion on the combustion chamber opening 20 side of thebase plate 2, but as an alternative for this, the firstthickness-increased portion 21 may be formed by attaching a shim platesubstantially equal in thickness to the base plate 2 to the end portionon the combustion chamber opening 20 side of the base plate 2 bywelding, for example. Or, the first thickness-increased portion 21 maybe formed by fitting a grommet over the end portion on the combustionchamber opening 20 side of the base plate, or by fitting a grommet overthe end portion on the combustion chamber opening 20 side of the baseplate 2 through the intermediary of an elastic plate, or by attachingshim plates formed as the full beads 6, 7 to the end portion on thecombustion chamber opening 20 side of the base plate 2 by welding, forexample.

Further, in the second embodiment, description has been made of anexample that the full beads 6, 7 formed on the outer side of the firstthickness-increased portion 21 of the base plate 2 and the full beads 6,7 are formed on the inner side of the second thickness-increased portion22 of the base plate 2. Then, the elastic sealing material is fixed tothe convex portions and is filled in the concave portions of the fullbeads 6, 7. However, this is not intended as a definition of the limitsof the invention, and on the inner side of the secondthickness-increased portion 22 of the base plate 2, in place of the fullbeads 6, 7, half beads each in a stepped structure may be formed bybending the base plate 2, and an elastic sealing material may be fixedto the convex portions and filled in the concave portions of the halfbeads. Further, on the outer side of the first thickness-increasedportion 21 of the base plate 2, in place of the full beads 6, 7, halfbeads each in a stepped structure may be formed by bending the baseplate 2, and an elastic sealing material may be fixed to the convexportions and filled in the concave portions of the half beads.

The elastic sealing material filled in the concave portions of the halfbeads is so formed as to be substantially flush with the flat surface ofthe base plate 2, and therefore the elastic sealing material is notexposed to cooling water, but the elastic sealing material fixed to theconvex portions protrudes from the flat surface of the base plate 2 andis directly exposed to cooling water. In this case, by providing theelastic sealing material fixed to the convex portions with a wide width,the elastic sealing material in its entirety can be prevented fromdeteriorating, thereby ensuring its superior sealing performance.

Further, in the embodiment mentioned above, the height of the convexportions of the full beads 6, 7 is made a little higher than the firstthickness-increased portion 21 and substantially equal to the height ofthe elastic sealing material fixed to the convex portions, and theheight of the convex portions of the full beads 6, 7 is made a littlehigher than the second thickness-increased portion 22. However, theseare not necessarily required, and for example, the height of the convexportions of the full beads 6, 7 may be made a little lower than thefirst thickness-increased portion 21 so that the full beads 6, 7 areembedded in the elastic sealing material, and though this is not showngraphically, the convex portions of the full beads 6, 7 may protrudefrom the elastic sealing material. The same applies to the half beads,too.

Further, in the embodiment mentioned above, the surface of the elasticsealing material fixed to the convex portion side of the full beads 6, 7or the half beads is made substantially parallel with the flat surfaceof the base plate 2, but this is not necessarily required, and as longas the elastic sealing material can be compressed and deformed incooperation with the beads, various shapes may be adopted for theelastic sealing material.

Further, in the embodiment mentioned above, the elastic sealing materialfilled in the concave portions of the full beads 6, 7 or the half beadsis made substantially flush with the flat surface of the base plate 2,but as long as the elastic sealing material is compressed and deformedin the through-thickness direction in cooperation with the beads, theelastic sealing material may have a somewhat rough surface with respectto the flat surface of the base plate 2. For example, the elasticsealing material filled in the concave portion side of the full beads 6,7 may have a groove formed therein to permit the elastic sealingmaterial to deform easily.

Further, in the embodiment mentioned above, description has been made ofa case where the elastic sealing material fixed to the convex portionside of the full beads 6, 7 is disposed on both sides across the widthof the convex portion, but this arrangement is not intended as adefinition of the limits of the invention. For example, the elasticsealing material fixed to the convex portion side of the full beads 6, 7may be arranged only on the combustion chamber opening 20 side of thewidth of the convex portion. By this arrangement, the elastic sealingmaterial (rubber, for example) on the convex portion side is preventedfrom being exposed to cooling water or oil, which leads to betterdurability, and this structure is most suitable when the full beads 6, 7are close to bolt holes 5 or water holes 23. The width of the beads maybe varied in the circumferential direction to adjust the surfacepressure.

Further, in each of the embodiments mentioned above, the elastic sealingmaterial has been filled in the concave portions of the beads 6, 7 so asto be substantially flush with the flat surface of the base plate beforethe cylinder block and so on are fastened together with clamping bolts.However, alternatively, it is possible to fill the concave portions ofthe full beads 6, 7 with an elastic sealing material in an amountsubstantially equal to the capacities of the concave portions, andarrange for the elastic sealing material in the concave portions to becompressed and deformed so as to be substantially flush with the flatsurface of the base plate 2 when the engine is assembled by fasteningwith clamping bolts.

A lubricant, such as molybdenum disulfide, which provides sealing andsliding properties, may be applied to one or both surfaces of the baseplate 2 to prevent fretting caused by a displacement or knocking by athermal expansion difference between the engine and the gasket orvibration amplitude.

A third embodiment of the present invention will be described withreference to the drawings.

FIG. 13 is a plan view for explaining a metallic gasket according to thethird embodiment of the present invention. FIG. 14 is a sectional viewtaken along the line A—A in FIG. 13. FIG. 15 is a sectional view takenalong the line B—B in FIG. 1. FIG. 16 is a sectional view taken alongthe line C—C in FIG. 1. FIG. 17 is a sectional view taken along the lineD—D in FIG. 13. FIG. 18 is a sectional view taken along the line E—E inFIG. 13.

Description will be made of a metallic gasket according to the thirdembodiment.

The metallic gasket 1 according to the third embodiment is an example ofa gasket sandwiched between the joint surfaces of the cylinder head andthe cylinder block of an internal combustion engine. As the base plate 2of the metallic gasket 1, it is possible to cite thin metal plate, suchas stainless steel, soft steel, or aluminum, but description will bemade on the assumption that soft steel plate is used to provide a lessexpensive gasket. If thin metal plate of low rigidity, such as softsteel plate is used for the base plate 2, a sufficient seal performancecan be obtained, as described later.

Almost in the middle of the base plate 2, there is formed a largecombustion chamber openings 3 located at a position corresponding to thecombustion chamber bore where a combustion gas is made to explode. Afirst thickness-increased portion 21 with the largest thickness isformed by upwardly folding back the whole inner peripheral edge of thebase plate at the open tip of the combustion chamber opening 3, and bythis folded-back portion, a difference in thickness with the remainingportions of the gasket is provided. Designed to generate a largestsurface pressure when its main part made of metal is mounted between thejoint surfaces, the first thickness-increased portion 21 is capable ofsufficiently sealing a combustion gas with the highest of pressures tobe contained. Note that the formation of the first thickness-increasedportion 21 is not limited to folding back the metal plate as mentionedabove, but it is possible make it by using a grommet as in prior art.The thickness of the folded-back portion of the firstthickness-increased portion 21 is planned to equalize the sealing facepressure borne by the first thickness-increased portion formed in thecircumferential direction by varying (inflecting) its thickness in itsextending direction along the circumferential direction of thecombustion chamber opening 3 by forming a thin web region relativelythinner than the vicinity of the bolt holes 5 and a thick web regionbetween the bolt holes 5.

In a metallic gasket for a multicylindered engine, a secondthickness-increased portion is often formed by locally folding back theedge portion of the outer periphery of the base plate 2. In this thirdembodiment, however, since the gasket is for use in a single cylinder,the fastening bolt axial tension is small and the distance from thecombustion chamber opening 3 to the peripheral edge portion is short;therefore, the second thickness-increased portion is formed of awide-width rubber bead as a substitute for the secondthickness-increased portion made of metal as will be described later.Needless to say, the second thickness-increased portion of metal platemay be used.

A first seal line SL1 is provided in a manner to endlessly encircle thefirst thickness-increased portion 21 of the base plate 2. On the outerside of the first seal line SL1, there are formed the water holes 4, oilhole 24, and chain chamber hole 25. A second seal line SL2 is set alongthe outer peripheral edge of the base plate 2, and a third seal line SL3is set in a manner to surround the chain chamber hole 25 and the oilhole 24. Moreover, a fourth seal line SL4 is set in a manner to surroundthe water holes 4 as the liquid holes. The fourth seal line SL4encircling the water hole 4 is arranged in some place to surround aplurality of water holes with a single seal line. The overlappingportions of seal lines which are close to each other or run in parallelare combined into a single line.

A bead BD is formed along all seal lines SL1 to SL4. The bead BDaccording to this embodiment is a composite bead of a metal bead 6 or 8and a rubber bead 7 or 9 as shown in FIG. 14, for example.

The metal beads 6, 8 are full beads formed by bending the base plate 2so as to protrude to one surface side (upper surface) of the base plate2, and the height of the beads is set so as to be higher than the firstthickness-increased portion 21, and the bead generates a sealingpressure as it is deformed in the through-thickness direction.

The rubber bead 7 or 9 comprises elastic sealing material 7 a, 7 b or 9a, 9 b fixed to the surface of the convex portion side of the base plate2 of the metal bead 6 or 8, and elastic sealing material 7 c or 9 cfilled in the concave portion on the reverse side of the convex portionof the metal bead 6 or 8. The elastic sealing material may be composedof a corrosion-resistant and elastic material, i.e., a rubber material,such as fluororubber, NBR or silicon rubber, or a resin material or thelike.

The elastic sealing material 7 a, 7 b, 9 a, and 9 b arranged on theconvex portion side of the metal beads 6, 8 are fixed to the surface ofthe base plate 2 in a manner to cover at least both sides across thewidth of the metal beads 6, 8. Some of the rubber beads 7, 9 formedalong the outer peripheral edge of the base plate 2 are formed for abroad range to make them also serve as the second thickness-increasedportion as shown in FIG. 19.

The height of the elastic sealing material 7 a, 7 b, 9 a and 9 b fixedto the convex portion side of the metal bead 6, 8 is made to be equal orsubstantially equal to the height of the convex portions of the metalbeads 6, 8 and their top surface is made substantially parallel with theflat surface of the base plate 2. Note that the height of theabove-mentioned elastic sealing material 7 a, 7 b, 9 a, and 9 b may beset to be a little higher than the height of the convex portions of themetal beads 6, 8 provided, however, that this height must be a heightsuch that the compression-deformed amount regulated by the height of thefirst thickness-increased portion 21 is 35% or less (the knowncompression-deformed amount of a specific material, which does not giverise to buckling).

Meanwhile, the amount of the elastic sealing material 7 c and 9 c filledin the concave portions of the metal beads 6, 8 is made substantiallyequal to the capacities of the concave portions and their bottom surfaceis made substantially flush with the flat bottom surface of the baseplate 2.

Thin films 14, 15 composed of the same material as that of the elasticsealing material 7 a to 7 c, 9 a to 9 c are fixed to the upper and lowersurfaces of the base plate 2 along the seal line encircling at least thewater holes 4 as shown in FIGS. 14 and 15, for example, and also anotherof the above-mentioned film 16 is formed on the inside peripheralsurface (interior surface) of the water hole 4. As a result, thatportion of the base plate 2 which is located on the inner side of theseal line encircling the water hole is completely covered with therubber beads 7, 9 and the films 14, 15 and 16. In this process, in theelastic sealing material 7 c or 9 c filled in the concave portion, theheight of the portion integral with the film 15 is set at the sameheight as the film 15 to secure better continuity with the film 15. Inthe portion shown in the sectional view taken along the line A—A, thereare the films 14 and 15, but if the bead is provided in a manner tocover the whole vicinity of the water hole, those films are notrequired.

In the base plate 2 on the inner side of the seal line set so as tocollectively enclose multiple water holes 4, a small hole 17 is formedwhich is open to both surfaces of the base plate 2, and as shown in FIG.16, this hole 17 interconnects the films 14 and 15 covering bothsurfaces of the base plate to make it more difficult for the films 14and 15 to separate from the base plate 2.

Here, it is possible to arrange the seal line encircling the water hole4 so as to be closer to the peripheral edge of the water hole 4, and asshown in FIG. 15, arrange the elastic sealing material 7 b, 9 b locatednear the water hole 4 out of the elastic sealing material 7 a, 7 b, 9 aand 9 b on the convex portion side, in order for the sealing materialparts 7 b, 9 b to cover the base plate up to the peripheral edge of thewater hole 4.

When the film 16 is formed on the inside surface of the water hole 4,the diameter of the water hole 4 becomes smaller by the amount of thethickness of the film 16 as shown in FIG. 15.

Before the film is formed, the diameter of the water hole 4 in thegasket is set by deducting the amount of the film thickness of the films14, 15 from the final diameter of a completed water hole on theassumption that the diameter of the water hole becomes equal to thediameter of the water hole in a cylinder head, for example, after thefilm is formed. By this arrangement, the water flow channel is preventedfrom becoming narrow locally at the position of the gasket.

Description will next be made of the operation and the effect of themetallic gasket mentioned above.

When a metallic gasket 1 structured as described is disposed between theopposing joint surfaces of a cylinder block and a cylinder head andfastened with clamping bolts, the elastic sealing material 7 a, 7 b, 9a, 9 b and the elastic sealing material 7 c, 9 c that constitute therubber beads 7, 9 are compressed and deformed in the through-thicknessdirection in cooperation with the metal beads 6, 8, and at the end offastening, the largest surface pressure concentrates on and the largestload acts on the first thickness-increased portion 21 due to adifference in thickness between the first thickness-increased portion 21with the largest thickness of the base plate 2 and the remainingportions.

Therefore, a threefold seal is applied, which chiefly comprises thelargest surface pressure on the first thickness-increased portion 21,and the elastic resiliences of the beads BD (metal beads 6, 8 and rubberbeads 7, 9 ), and simultaneously the stopper effect of the firstthickness-increased portion 21 prevents total collapse of the elasticsealing material 7 a to 7 c and 9 a to 9 c fixed or filled on the convexportion side or on the concave portion side of the metal beads 6, 8, andthe stopper effect of the second thickness-increased portion 22 preventstotal collapse of the elastic sealing material 7 a to 7 c and 9 a to 9 cfixed or filled on the convex portion side or on the concave portionside of the metal beads 6, 8.

Further, since the water hole 4 is enclosed by the beads BD structuredas described, cooling water is prevented from moving to the outer sideof the beads BD.

In the metallic gasket 1 structured as described, too, since the elasticsealing material 7 a, 7 b, 9 a, 9 b are fixed to the convex portions ofthe metal beads 6, 8 and the like elastic sealing material 7 c, 9 c arefilled in the concave portions of the metal beads 6, 8, the elasticsealing material 7 a, 7 b, 9 a, 9 b that protrude from the base plate 2in the through-thickness direction is the elastic material parts only onthe convex portion side of the metal beads 6, 8, in other words, on oneside of the base plate 2.

Therefore, the height of the elastic sealing material 7 a, 7 b, 9 a, 9 bfixed to the convex portions of the metal beads 6, 8, for example, is(t0 t1)+the compression-deformed amount ((t0 t1)

0.4 (40% max.)) if the thickness of the base plate 2 is designated as t1and the thickness of the first thickness-increased portion 21 isdesignated as to, and assuming that t0 is 0.5 mm, the thickness of thebase plate t1 is 0.25 mm (in this embodiment, the thickness ti of thebase plate is set at ½ of to because the first thickness-increasedportion 21 is formed by folding back the base plate 2.), the height ofthe rubber beads 7, 9 is 0.35 mm from the above equation, which is 1.7times the value in prior art shown in FIG. 25.

Therefore, the elastic sealing material 7 a, 7 b, 9 a, 9 b on the convexportions of the metal beads 6, 8 increases in quantity, and theircompression-deformed amounts become larger, making it easy to carry outa forming process of the elastic sealing material 7 a, 7 b, 9 a, 9 b,and making it possible to increase the thickness of the elastic sealingmaterial 7 a to 7 c and 9 a to 9 c, so that it becomes possible to set alarger processing tolerance and reduce manufacturing cost.

Out of the elastic sealing material 7 a, 7 b, 9 a, 9 b fixed to bothsides across the width of the convex portions of the metal beads 6, 8,only the parts 7 b, 9 b facing the water hole 4 are exposed to coolingwater. On the other hand, the elastic sealing material 7 c, 9 c filledin the concave portions of the metal beads 6, 8 are covered with themetal beads 6, 8 and are not exposed to cooling water, for which reasonthe elastic sealing material 7 a, 7 c, 9 a, 9 c are protected fromdeterioration and therefore can maintain a stable seal performance for along period of time.

In addition, since the whole surfaces (the upper and lower surfaces thebase plate and the inside surface of the hole) of the base plate 2within the seal line SL4 formed in a manner to surround the water hole 4are covered with the corrosion-resistant films 14 and 15, the base plate2 is prevented from being corroded even if a liquid likely to corrodethe base plate 2 happens to flow through the water hole 4, such assubstandard cooling water.

Further, a required sealing pressure is obtained by synergy of theresilience of the metal beads 6, 8 and the elastic resilience of theelastic sealing material 7 a to 7 c and 9 a to 9 c fixed to the convexportions or filled in the concave portions of the metal beads 6, 8, afact which makes it possible to decrease the hardness of the base plate2 itself, therefore eliminate worries about fatigue failure of the beads6, 8 of the base plate 2, moreover absorb the engine vibration amplitudeand the seal area roughness, and thereby sufficiently seal cooling waterpressure and oil pressure with a lower surface pressure.

Further, since a wide sealing area can be secured for the elasticsealing material 7 a, 7 b, 9 a, 9 b on the convex portion side and alsofor the elastic sealing material 7 c, 9 c on the concave portion side ofthe metal beads 6, 8, in other words, since the portions of the gasketwhich serve as the area seal and contact the joint surfaces are made ofrubber or a rubber-based material, the flaws and the blowholes ascasting defects on the joint surfaces or the roughness of the processedsurfaces can be sealed satisfactorily with a low surface pressure. Inaddition, since the elastic sealing material 7 a to 7 c and 9 a to 9 cconsist of an elastic material (rubber-based, above all else), thegasket factor is low, and therefore a limited axial load can be utilizedeffectively in the regions under adverse condition, and total load canbe decreased.

Further, the first thickness-increased portion 21 of the base plate 2 ismade a thin web area in the vicinity of bolt holes 5, but it is made athick web area between the bolt holes 5 such that the resilience of thefirst thickness-increased portion 21 is weak in the vicinity of clampingbolts whose fastening force is large; however, the resilience isstronger in the area between the clamping bolts whose fastening force isrelatively small. Consequently, the surface pressure applied to thefirst thickness-increased portion 21 can be equalized in thecircumferential direction of the combustion chamber opening 3, and theaxial tension of the clamping bolts can be decreased, thus making itpossible to satisfactorily prevent deformation of the engine,particularly in engines of low rigidity. Recently, progresses have beenmade to engines in terms of reductions in size and weight and highperformance, and as lean fuel is burned for energy saving, combustionchamber temperature has risen. To seal a high pressure gas, a highsurface pressure is generated by the first thickness-increased portion21 which is formed by folding back the inner peripheral edge on thecombustion chamber opening 3 side of the base plate as mentioned above.In this embodiment, by varying the thickness in the circumferentialdirection of the first thickness-increased portion 21, the fasteningsurface pressure along the peripheral portion of the opening for thecombustion chamber bore is equalized, reducing oil consumption and powerloss, thereby improving the efficiency of sealing a combustion gas.

In this embodiment, convex cross-section beads 6, 8 are provided ifnecessary in a manner to surround the first thickness-increased portion21 in the peripheral portion of the combustion chamber opening 3 andalso surrounding the oil hole 24, water holes 4, bolt holes 5 and achain chamber hole 25. With the convex cross-section metal beads 6, 8,the bead height or the bead width may be varied according to therigidity of the joint surfaces at positions of contact to equalize thesealing pressure along the seal lines to thereby improve the sealefficiency. The sealing pressure can be equalized more easily by raisingthe bead height or widening the bead width at positions where therigidity is insufficient and the surface pressure is weak.

Here, by forming films on the outer side of the bead BD as shown inFIGS. 20 and 21, which depict the outer peripheral edge, corrosion fromcontact with filthy water or salt water or the like is prevented.

The structure of the metallic gasket according to this invention is notlimited to the above embodiment, but may be changed with properdiscretion without departing from the scope and spirit of the invention.

Further, in the embodiment mentioned above, the firstthickness-increased portion 21 is formed by folding back the innerperipheral end portion on the combustion chamber opening 3 side of thebase plate 2, but as an alternative for this, the firstthickness-increased portion 21 may be formed by attaching a shim platesubstantially equal in thickness to the base plate 2 to the end portionon the combustion chamber opening 3 side of the base plate 2 by welding,for example. Or, the first thickness-increased portion 21 may be formedby fitting a grommet over the end portion on the combustion chamberopening 3 side of the base plate, or by fitting a grommet over the endportion on the combustion chamber opening 3 side of the base plate 2through the intermediary of an elastic plate, or by attaching shimplates formed as the fall beads 6, 8 to the end portion on thecombustion chamber opening 3 side of the base plate 2 by welding, forexample.

Further, in place of the metal beads 6, 8 as full beads, metal beads 29may be formed as half beads each in a stepped structure by bending thebase plate 2 as shown in FIG. 22, and elastic sealing material 30, 31may be fixed to the convex portion of or filled in the concave portionof each of the metal beads 29.

Here, since the elastic sealing material 30 filled in the concaveportion of the metal bead 29 as a half bead has its bottom surfacesubstantially flush with the flat bottom surface of the base plate 2,the elastic sealing material 30 is hardly exposed to cooling water. Theelastic sealing material 31 fixed to the convex portion side extends inthe through-thickness direction and is therefore directly exposed tocooling water. In this case, the width of the elastic sealing material 7a, 7 b, 9 a, 9 b is widened to prevent deterioration of all of thesealing material parts 7 a, 7 b, 9 a, 9 b to thereby secure asatisfactory seal performance.

Further, in the embodiment mentioned above, the top surface of theelastic sealing material 7 a, 7 b, 9, 9 b fixed to the convex portionsof the metal beads 6, 8 is made substantially parallel with the flatsurface of the base plate 2, but this is not necessarily required, andit is possible to adopt various shapes as long as the sealing materialparts can be compressed and deformed in the through-thickness directionin cooperation with the metal beads 6, 8.

Further, in the embodiment mentioned above, the elastic sealing material7 c, 9 c filled in the concave portions of the metal beads 6, 8 are madesubstantially flush with the flat surface of the base plate 2, but theelastic sealing material 7 c, 9 c may have a somewhat irregular surfacewith respect to the flat surface of the base plate 2 as long as thesealing material parts be compressed and deformed in thethrough-thickness direction in cooperation with the metal beads 6, 8.For example, a groove may be formed in the elastic sealing material 7 c,9 c filled in the concave portion side of the metal beads 6, 8 to permitthe sealing material parts 7 c, 9 c to deform easily.

As shown in FIGS. 23 and 24, a second thickness-increased portion ofmetal may be formed by folding back a part of the outer peripheral edgeof the base plate 2.

The elastic sealing material 7 a to 7 c, 9 a to 9 c, 30 and 31 thatconstitute the rubber beads mentioned above may be formed by fixing tothe convex portion side or filling in the concave portion side of thebeads 6, 8 of the base plate 2. For this purpose, passages (not shown)for a molding material may be formed in the metal beads 6, 8, forexample, for simultaneous forming of the convex and concave portions.

The earlier-mentioned films may be formed by chromium plating, forexample.

Though description is being made referring chiefly to a water-cooledengine, with an air-cooled engine, the bead line on the outer side ofthe first thickness-increased portion 21 can be done away with.

A fourth embodiment of the present invention will be described withreference to the drawings.

In the metallic gasket 1 according to the invention in the presentapplication, the structure other than that of the beads along the seallines are the same for each of the above-mentioned embodiments.

In other words, the beads are formed along the seal lines SL1 and SL2.

As shown in FIGS. 25 and 26, the bead BD in this embodiment is acomposite of one bead 6 made of the base plate as a full bead and onerubber bead 8 or 10.

The base-plate bead 6 is formed on the thickness-increased portion 16side by bending the base plate 2 in the through-thickness direction andis in a convex form with a height higher than the thickness-increasedportion 16.

The rubber bead is composed of a first elastic sealing material 10filled in the concave portion of the base-plate bead 6 and a secondelastic sealing material 8 fixed to the convex portion side of thebase-plate bead 6.

The first elastic sealing material part is arranged so that the bottomsurface is flat and substantially flush with the bottom surface of thebase plate 2. In about the center in the width direction of the bead, aconvex protrusion 11 is formed on its bottom surface in a manner toextend along the seal line SL1 or SL2.

The second elastic sealing material 8 is formed with a width slightlywider than the width of the base-plate bead 6 and on the surface of theconvex portion of the bead and on the flat surface continuous to theconvex portion. The second elastic sealing material 8 is designed sothat its height is almost equal to the height of the base-plate bead 6and the surface (the top surface) is substantially flat.

The width of the second elastic sealing material 8 is preferably notmore than 1.5 times the width of the base-plate bead 6. If the width isincreased excessively, load increases excessively. The height of theelastic sealing material 8 is preferably in the range of 0.9 to 1.1times the height of the base-plate bead 6.

The number and the kinds of holes, such as the bolt holes 5 formed inthe base plate 2, and the location of the seal lines SL1 and SL2naturally differ with the kind of a cylinder block and a cylinder headbetween which the metallic gasket 1 is disposed.

The metallic gasket 1 structured as described is set in place when it isdisposed between the joint surfaces of the cylinder block and thecylinder head of an engine and fastened with clamping bolts. The beadsare deformed by the fastening force of the clamping bolts and a requiredsealing pressure is generated along the seal lines to thereby seal oiland so on.

When the gasket is fastened, the thickness-increased portions 16provided at the peripheral end portion of the combustion chamber opening3 serve to limit the compression-deformed amount of the beads, a highsurface pressure occurs at the thickness-increased portions 16, so thatthe thickness-increased portion 16 seals a combustion gas at hightemperature and high pressure.

When no coating is applied to the surface of the thickness-increasedportion 16 to supply the gasket at a low price, the thickness-increasedportion 16 of the gasket comes into metal-to-metal contact with themachined surfaces Joint surfaces) of the engine, and consequently thereis a tool-mark irregularity of 3 to 6 microns on the machined surfaces.

The explosion pressure by engine operation is not a constantly-appliedpressure but a pulsating pressure; therefore, there is some pressureleakage from the thickness-increased portion 16 to the outer peripheryside. However, the pressure is sealed by the bead BD on the outer sideof the thickness-increased portion 16.

The bead BD according to this embodiment is so structured as to generatea required sealing pressure by a composite spring of the base-plate bead6 and the rubber bead produced when they are compressed and deformed,and this composite structure makes it possible to reduce the hardness ofthe base plate 2 that forms the base-plate bead 6. The beads contact theupper and lower joint surfaces at the flat surfaces of the compressedand deformed elastic sealing material 8 and 10, and the soft elasticsealing material 8 and 10 come into tight contact with the jointsurfaces, closing any small spaces of the tool marks, thereby sealingthe combustion gas that leaks from the thickness-increased portion 16under pulsating pressure mentioned above.

In a gasket of a structure that an elastic sealing material is filledonly in the concave portion of the base-plate bead 6, when the elasticsealing material 10 is compressed and deformed, an external force isgenerated to deform the base-plate bead 6 and the flat portion on eachside continuous to the base-plate bead 6 in such a manner that they warpupward. The lower the hardness of the base plate 2 is made to inhibitfatigue failure of the base-plate bead 6 and hold down the cost of thebase plate 2, the more conspicuous the deformation, such as upward warpis likely to become. In this embodiment, the second elastic sealingmaterial 8 is provided also on the convex portion side to let the secondelastic sealing material 8 be deformed to prevent deformation of thebase-plate bead 6 and the base plate 2, thereby preventing thedeterioration of the seal performance by the first elastic sealingmaterial 10 in the concave portion.

In the filling of the first elastic sealing material 10, the centerportion of it is likely to cave in a little in a tnansition from hightemperature to open cooling. In this embodiment, protrusions 11 and 9are formed, even when the gasket is adopted in an engine whose fasteningaxial tension is weak, a stable seal performance can be secured at lowlost in the region on the outer side of the combustion chamber opening3. After the bolts are fastened, the protrusions 11 and 9 are in acrushed and flattened state.

No fastening problem arises in the vicinity of bolts 4 is free of aslong as the bolts are fastened properly. However, the oil holes 5 andthe chain chamber hole 17 are in an improperly fastened state becausethey are remote from clamping bolts. As the engine is subjected torepeated thermal cycles as many times as it is used, the fastening axialtension decreases to some extent. The gasket is deformed by heat duringengine operation, thus aggravating the sealing condition.

In order to implement a complete seal under those adverse conditions, inthe prior art, in the bead structure having the elastic sealing material10 filled in the concave portion of the base-plate bead 6, if thehardness of the base plate 2 is increased, the spring force isincreased, but the bead may suffer fatigue failure by vibrationamplitude, and it is not desirable to increase the hardness so much; onthe other hand, if the hardness of the base-plate bead 6 is decreased,deformation mentioned above will occur, resulting in a decrease in thespring force. To make up for this shortcoming, in this embodiment, asdescribed above, in addition to the first elastic sealing material 10filled in the concave portion of the base-plate bead 6, the secondelastic sealing material 8 is formed on the convex portion on thereverse side of the concave portion, and the second elastic sealingmaterial 8, structured such that its width is wider than the width ofthe bead and its height is substantially the same height of thebase-plate bead 6, serves to prevent deformation of the base plate 2 andthe base-plate bead 6.

As the hardness of the base plate 2 is lowered, the spring force is madelow, but because the first elastic sealing material 8 is formed, on theconvex portion, with a height equal to the height of the base-plate bead6 to thereby regulate the deformation by the elastic sealing material 10filled in the concave portion, with the result that the BD bead isprovided with a spring force equal to or greater than a spring force bya structure that uses the base plate 2 of a high-hardness material.

Further, when the elastic sealing material 10 is formed by molding, theconcave portion side of the base-plate bead 6 is processed so as to beflush with the flat surface of the base plate 2. During molding, thesealing material 10 expands thermally by high temperature, but when itis open-cooled, the central portion of the rubber large in thicknessshrinks by an amount corresponding to thermal expansion, and caves inslightly, and in the portions, away from a clamping bolt, which are notfastened properly and overhang, the surface pressure may decrease,leaving chances of pressure leak.

As countermeasures, according to the invention in this patentapplication, as shown in FIG. 25, a small protrusion 11 is formed in themiddle of the surface of the elastic sealing material 10 in the concaveportion of the base plate 6, the bead is deformed without increasing thefastening load so much, and when the surface pressure decreases, theprotrusion 11 formed on the surface of the first elastic sealingmaterial 10 bulges and deforms concurrently. Though small in terms ofarea, the protrusion generates a high surface pressure, and serves toapply a complete seal. In other words, located in a position away fromthe clamping bolt to the outer periphery side, the surface pressuretends to become relatively small, the elastic sealing material on bothsurfaces of the base-plate bead 6 is normally pressed to the opposedjoint surfaces to seal them by the compressed and deformation of thebead by the fastening load. At this time, the protrusion 11 formed onthe elastic sealing material 10 on the concave portion side is deformedin a manner to be pushed into the concave portion, adapts itself to theflat surface of the joint surface, and becomes substantially flush withthe flat surface (underside) of the base plate 2.

When, from this steady state, the clearance between the opposed jointsurfaces at the bead position increases by vibration, for example, thesurface pressure temporarily decreases, the compression-deformed amountof the bead decreases, thus reducing the sealing pressure. At theelastic sealing material 10 on the concave portion side, according to anincrease in the clearance, the protrusion 11 automatically bulges tosecurely retain contact with the opposite joint surface and has thecontact surface decreased, and can maintain the seal condition by anincrease in the surface pressure by the protrusion. As the clearancedecreases, the steady state is restored.

In the foregoing, description has been made of a case where the surfacepressure decreases with changes in the clearance between the opposedjoint surfaces. Even when the clearance between the opposed jointsurfaces remain unchanged or even when the spring force decreases withdeterioration with time and the surface pressure becomes smaller, asdescribed above, because load concentrates on the protrusion 11 as thesurface pressure decreases (the protrusions 11 and 9 do not necessarilybulge in this case), the surface pressure rises at the position of theprotrusion 11, making it possible to maintain a specified sealingpressure.

When the change in the gap at the bead position between the jointsurfaces is large, it is preferable to form a protrusion 9 also on theelastic sealing material on the convex portion of the base-plate bead 6as shown in FIG. 27.

The protrusions 11, 9 arranged in the bead-width direction are notlimited to one, and may be two or more as shown in FIGS. 28 to 30. Whentwo or more protrusions are provided, the height of the protrusions 11,9 may be made different. The magnitude of the protrusions may also bedifferent. When a plurality of protrusions are formed, load of surfacepressure can be alleviated, or if the surface pressure decreases, alabyrinth effect may be obtained by the plurality of protrusions 11, 9or the de facto increase of the seal lines SL provides an effect of astable sealing property for an extended period of time.

Further, with regard to the plurality of protrusions 11, 9, by makingvariations in the size or shape (the area unit length in a longitudinalsectional profile or a plan view) of the protrusions 11, 9 to seekoptimization of the protrusions 11, 8 as shown in FIGS. 31 to 34, it ispossible to enlarge the above-mentioned effects. In other words, whenproviding two or more protrusions in parallel widthwise, it ispreferable to make the height of the protrusions 11, 9 relatively low orreduce the area per unit length on the higher surface pressure side.

With regard to a single-line protrusion 11, 9 extending along the sealline, it is possible to change the height or shape of the protrusion 11,9 according to the surface pressure at the location of the protrusion11, 9. In other words, in the areas where the surface pressure isrelatively smaller, the height and the width of the protrusion 11, 9 maybe increased.

The protrusions 11, 9 may be formed continuously along the whole lengthof the seal lines SL1 and SL2 or intermittently at specified intervals.

When the protrusions 11, 9 are formed partly on the seal lines SL1, SL2,they should be formed at positions that are far from the bolt hole andat relatively low surface pressure or at parts where changes in theclearance between the opposed joint surfaces are relatively large (theamplitude of surface pressure change is relatively large).

In this embodiment, description has been made of the base-plate bead 6as a full bead, but this embodiment is applicable when the base-platebead 6 is a half bead in a stepped structure. More specifically, asshown in FIGS. 35 and 36, a second elastic sealing material 12 is fixedto the convex portion (the portion rising from the flat part of the baseplate) of the base-plate bead 6 in a stepped form, a first elasticsealing material 14 is applied to the concave portion on the reverseside of the convex portion, and then protrusions 13, 15 are formed atthe thick portions. The operation and the effect are the same as in theabove-mentioned embodiment.

In the bead BD in the vicinity of the thickness-increased portion 16,the second elastic sealing material need not necessarily be attached toboth sloped sides of the convex portion as shown in FIG. 37. In otherwords, receiving a relatively high surface pressure and having a strongforce to constrain the base plate, the thickness-increased portion 16inhibits the base plate from being deformed. This applies to theportions in the vicinity of clamping bolts.

The height of the protrusions 11, 9 should be designed such that thedeformation ratio is not more than 25% when the protrusions are deformedto reach the thickness of the thickness-increased portion 16, regardlessof the shape of protrusions.

In the above example, description has been made of a metallic gaskethaving a single base plate. In a metallic gasket, a plurality of baseplates, each having the above-mentioned structure, may be stacked oneover another according to the space between the joint surfaces. In thiscase, the base plates need not necessarily be stacked such that theconvex portions of the base-plate beads are arranged face-to-face witheach other as in prior art.

The other aspects of the structure, the operation and the effect are thesame as in the above-mentioned embodiments.

INDUSTRIAL APPLICABILITY

As is clear from the above description, by adopting this invention, itis possible to obtain a metallic gasket which exhibits rust-preventingeffects by blocking infiltration of moisture, such as salt water, fromthe outside, and which can securely maintain a satisfactory sealingproperty for an extended period of time under the conditions, such assealing-surface roughness, as in engines of violent vibration amplitude,repetition of high and low temperatures, low surface pressure infastening.

1. A metallic gasket comprising a base plate made of a thin metal plate,said base plate having formed therein one or not less than two openingsand a metal bead of a convex cross-section formed along seal lines bybending said base plate in the through-thickness direction, said metalbead being deformed in the through-thickness direction to seal a jointof opposing joint surfaces when said metallic gasket is sandwichedbetween said joint surfaces, wherein an elastic sealing materialdeformable under compression in cooperation with deformation of saidmetal bead is fixed at least to a convex portion of said metal bead andis filled in a concave portion on the reverse side of said convexportion, and the height of said elastic sealing material on a surface ofsaid convex portion side is made equal to or substantially equal to theheight of said convex portion, and wherein on the surface of said baseplate on said convex portion side of said metal bead, said elasticsealing material deformable under compression in cooperation with thedeformation of said metal bead is fixed also to portions of said surfaceof the base metal facing at least one of an outer peripheral edge ofsaid joint surface and an inner peripheral portion of an opening of saidjoint surface opposite said surface of the base plate and wherein to thewhole peripheral edge of or a part thereof in an least one of an innerperipheral edge of said hole formed in said base plate and an outerperipheral edge of said base plate, a thickness-increased portion isformed by upwardly folding back at least one of said inner peripheraledge of said hole and said outer peripheral edge of said base plate,with a thickness higher than the remaining areas of said base plate andlower than said convex portion of said metal bead to regulate thedeformed amount in the through-thickness direction of said elasticsealing material.
 2. A metallic gasket according to claim 1, whereinsaid metal bead is a full bead or a half bead in a stopped form.
 3. Ametallic gasket according to claim 1, wherein by partly varying at leastone of a height of said protrusion and the width of said metal width inthe extending direction of said metal bead, the sealing surface pressureis equalized in the extending direction of said bead.
 4. A metallicgasket according to claim 1, wherein said metal bead is formed along atleast one of an inner peripheral edge of an opening formed in said baseplate and an outer peripheral edge of said base plate.
 5. A metallicgasket according to claim 1, wherein at least a part of an outerperipheral edge of said base plate extends beyond said opposing jointsurface to the outside.
 6. A metallic gasket according to claim 1,wherein a thin corrosion-resistant film thinner than said elasticsealing material is fixed to areas not covered with said elastic sealingmaterial at least on one surface of said base plate.
 7. A metallicgasket according to claim 1, wherein one or not less than two lines ofprotrusions are formed along said seal line on at least one of saidelastic sealing material fixed to the surface of said convex portionside and the surface of said elastic sealing material filled in saidconcave portion.
 8. A metallic gasket according to claim 7, wherein atleast one of the height and the width of each line of said protrusionsin the extending direction thereof is varied according to said sealingsurface pressure at a formed position of said protrusion, and as saidsealing surface pressure becomes small, a larger value is set for atleast one of the height and the width of said protrusions.
 9. A metallicgasket according to claim 7, wherein a plurality of lines of protrusionsare formed on at least one of the surface of said elastic sealingmaterial fixed to said convex portion side and on the surface of saidelastic sealing material filled in said concave portion, and wherein inthe plurality of lines of said protrusions, at least one of an area perheight of said protrusion and an area per unit length of said protrusionis varied according to said sealing surface pressure at a formedposition of said protrusion.
 10. A metallic gasket according to claim 7,wherein a plurality of base plates are stacked in a multilayeredstructure.
 11. A metallic gasket according to claim 1, wherein one ornot less than two lines of protrusions are formed in areas where saidsealing surface pressure is relatively low at least on one of thesurface of said elastic sealing material fixed to the surface of saidconvex portion side and the surface of said elastic sealing materialfilled in said concave portion.
 12. A metallic gasket comprising a baseplate made of a thin metal plate having at least a combustion chamberopening and a liquid hole, a thickness-increased portion formed at aninner peripheral edge on said combustion chamber opening side of saidbase plate, and a bead formed along a seal line for sealing by deformingin the through-thickness direction, wherein at least a part of said sealline is arranged in a manner to encircle one or not less than two liquidholes, wherein a bead formed along said seal line encircling at leastsaid liquid hole comprises a metal bead formed in a convex form with aheight higher than the thickness-increased portion by bending said baseplate in the through-thickness direction, and a rubber bead made of anelastic sealing material fixed to the surface on said convex portionside of said metal bead of said base plate or filled in a concaveportion on the reverse side of said convex portion, wherein said elasticsealing material on the surface of said convex portion side is fixed atleast to the surface of said convex portion of said metal bead and isarranged to be equal or substantially equal in height to said metalbead, and wherein a corrosion-resistant film is formed on the surface ofsaid base plate surrounded by said bead formed along said seal lineencircling said liquid hole on said convex portion side of said metalbead and said film has a height lower than the height of said rubberbead, and wherein said thickness-increased portion is formed by upwardlyfolding back said inner peripheral edge on said combustion chamberopening side of said base plate thereby generating a high surfacepressure.
 13. A metallic gasket according to claim 12, wherein a thin,corrosion-resistant film is formed on the surface surrounded by saidbead formed along said seal line on said concave portion side of saidmetal bead, and said film is continuous to said elastic sealing materialfilled in said concave portion.
 14. A metallic gasket according to claim13, wherein a plurality of through-holes are formed at positions of saidbase plate surrounded by said bead formed along said seal lineencircling said liquid hole, and said films formed on both surfaces ofsaid base plate are connected through said plurality of through-holes.15. A metallic gasket according to claim 12, wherein said film is alsoapplied to the inside peripheral surface of said liquid hole.
 16. Ametallic gasket according to claim 15, wherein at least a part of saidbead formed along said seal line encircling said liquid hole is arrangedalong the whole peripheral edge of said liquid hole, said elasticsealing material on said convex side is arranged up to said filmcontinuous to said elastic sealing material on said convex side isapplied to said inside peripheral surface of said liquid hole, and thatthe size of said liquid hole including an amount corresponding to saidthickness of said film is substantially equal to the size of said liquidhole open to said joint surfaces to be sealed by said gasket sandwichedtherebetween.
 17. A metallic gasket according to claim 12, wherein asecond thickness-increased portion is also formed by upwardly foldingback a part of said outer peripheral edge of said base plate, and saidseal line extending along said outer peripheral edge is arranged at theouter peripheral edge of the base plate or in the vicinity of said outerperipheral edge, excluding said second thickness-increased portion,wherein said bead formed along said seal line comprises a metal beadformed in a convex form higher than the height of saidthickness-increased portion by bending said base plate in thethrough-thickness direction, and a rubber bead made of an elasticsealing material fixed to the surface of said convex portion side ofsaid metal bead of said base plate and filled in said concave portionand compressed and deformed in the through-thickness direction incooperation with the deformation of said metal bead, said elasticsealing material on the surface of said convex side is fixed at least tothe surface of said convex portion of said metal bead, and the height ofsaid elastic sealing material is arranged to be equal or substantiallyequal to the height of said metal bead.
 18. A metallic gasket accordingto claim 17, wherein said second thickness-increased portion is omitted,and to substitute for said second thickness-increased portion, awide-width portion is provided in part along said rubber bead in theextending direction of said rubber bead.
 19. A metallic gasket accordingto claim 18, wherein in a corrosion-resistant film is formed on thewhole surface of said base plate on the outer side of said seal linealong said outer peripheral edge of said base plate.